Melt butter in a medium saucepan on medium heat. Add milk, stirring occasionally, until it is warm. Turn off heat.

Whisk flour and baking powder in a small bowl. Set aside.

In a deep mixing bowl, beat eggs for 1 minute. Slowly add sugar, 1 cup at a time. Continue beating for 1 minute after the last addition. Add vanilla extract and lemon zest. Blend. Slowly add half of the flour mixture, followed by about 1 cup of the milk mixture, beating for about 30 seconds after the milk addition. Add the rest of the flour, then all of the remaining milk mixture. Beat for just over 1 minute. The batter will be watery and will splash. Angling a large paper plate over the bowl with help contain the splashing.

Divide batter equally (not an exact science—just eye-ball this) into three separate bowls. Add a few drops of green food coloring to one bowl and red to another bowl (I use about 1/8 teaspoon of gel food coloring). Whisk thoroughly to blend. Add more if needed to obtain desired color. The third bowl remains undyed.